1. Field of the Invention
The present invention relates to a digital camera, electronic equipment with a photographing function, and so on. In particular, it relates to a recording process of image data.
2. Description of the Related Art
In a digital camera, or a cellular phone with a photographing function, image data is encoded to decrease the amount of image data. High-quality image data, such as “RAW data”, can be encoded or compressed and recorded in a memory in accordance with a lossless (compression) coding. Thus, the original image data can be completely reconstructed from the compressed image data without information loss. In the JPEG lossless coding, a spatial coding is applied, wherein a difference value between neighboring pixels is successively calculated in accordance with the DPCM (Differential Pulse Code Modulation) fashion, and the difference value is subjected to the Huffman-Coding.
In the case of lossless coding, the amount of data to be recorded increases significantly when compared to a lossy (compression) coding with information loss. To decrease the amount of compressed data, for example, a plurality of Huffman Tables is prepared and the image data is encoded in each Huffman Table. Then, the smallest amount of minimum encoded data is selected.
The lossless coding uses a predictive coding process wherein a sample pixel is predicted from neighboring pixels. This process is based on the condition or assumption that neighboring pixels have a high correlation with respect to pixel values. When a low correlation between neighboring pixels exists, such as a checkered-pattern image, the amount of compressed image data obtained by lossless coding is occasionally larger than that of original uncompressed image data.
On the other hand, when photographing, especially when carrying out a continuous shooting, shorting of the compression process and recording process is required to capture as many images as possible. However, the lossless coding cannot effectively shorten the time necessary for recording image data because of the large amount of data to be recorded.